Just got word from Apple that this issue is going to be filed as a bug with normal priority and that it will be taking weeks before it is going to be fixed. Furthermore I was told, that even phone support started giving out the temporary solution I found with SwitchResX. So it is time to give a short howto here on using SwitchResX with a TFT display connected to your Mac via DVI or HDMI:
01. Download SwitchResX Universal Installer: http://madrau.com/html/SRX/DL.shtml (current version is 3.8.6)
02. Unzip it.
03. Install it by double-clicking the SwitchResX Installer and following the instructions. It will automatically lauch the program on completion, if you do not tamper with the Installer's default settings.
04. In the window named "SwitchResX Control" click on the custom tab.
05. Click on the plus ("+") button at the bottom left of the window to add a new configuration. A window will pop up called "Timing Parameters".
06. Make sure the drop-down list in the upper left corner is set to "custom".
07. Check "use simplified settings" at the bottom of the window, then select "CVT-RB" from the now activated drop-down list.
08. Enter your native horizontal resolution in the first field below the "Horizontal" column title (e.g. "1920", no quotes!).
09. Enter your native vertical resolution in the first field below the "Vertical" column title (e.g. "1200", no quotes!).
10. Make sure that "Interlaced" is unchecked (top right).
11. Confirm that your vertical Scan rate matches a value something near to 60 Hz. (It does not necessarily match exactly 60 Hz, since my Belinea o.displays clock at 59,997 Hz for example.)
12. Check "Positive sync" in both "Horizontal" and "Vertical" columns.
13. Click "Ok". (window closes)
14. Back in the previous window, you should now see a new resolution entry matching the values you just entered.
15. Click "Apply"
16. Close the window and reboot your machine.
17. Once restarted, open up System Preferences and choose Apple's original "Monitor" preferences.
18. In the "Monitor" tab, you should now be able to choose the newly added resolution.
19. If your screen does not scale the image, try checking "Overscan" from within the "Options" tab.
20. Fingers crossed, you should be all set. Maybe you need to do a final reboot.
21. You can safely deinstall ScreenResX after the process and the fixed resolution will still stay on. Or you can decide to give Stephane (the author) some credit for his great tool and buy a copy.